KERS 3, but (sometimes) no strong over-run drag of motor braking

Hi,
I always drive using the Eco-mode and with the Kinetic Energy Recovery System (KERS) at level 3.
But sometime, especially the first couple of miles, there is no (strong) motor braking.
In these moments, it feels like there is a hidden clutch pedal and someone is pressing on it..

How is that? Does anyone have an idea?

The driver can select three energy regeneration levels by operating the KERS switch :
KERS 3: Heavy Heavy Level: Maximum energy is regenerated, the vehicle exhibits shorter coasting distances and a strong sensation of over-run drag or motor braking. The message centre displays KERS 3

If the battery is either very full (above 95%) or very cold, it cannot take the recovered energy, so the KERS effect is reduced and you need to use the regular brakes more.

Agreed: high SoC and/or low battery temp limits or prevents full regen to prevent battery damage.

aserraric said:

If the battery is either very full (above 95%) or very cold, it cannot take the recovered energy, so the KERS effect is reduced and you need to use the regular brakes more.

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Thanks, this is helpful, because that is/was indeed the case!

PaulC82 said:

Agreed: high SoC and/or low battery temp limits or prevents full regen to prevent battery damage.

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And with SoC this relate to the State of charge (SoC)? And with a low battery temperature. Thanks

Stefann said:

And with SoC this relate to the State of charge (SoC)? And with a low battery temperature. Thanks

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In my FL5 KERS 3 behaves like KERS 1 when I drive off with a full battery.

It is much the same as if you are charging a battery with a battery charger. As the battery nears fully charged, the charging current reduces to virtually nil.

crispyjay said:

In my FL5 KERS 3 behaves like KERS 1 when I drive off with a full battery.

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FL5?

blippy said:

FL5?

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FaceLift MG5

Stefann said:

Hi,
I always drive using the Eco-mode and with the Kinetic Energy Recovery System (KERS) at level 3.
But sometime, especially the first couple of miles, there is no (strong) motor braking.
In these moments, it feels like there is a hidden clutch pedal and someone is pressing on it..

How is that? Does anyone have an idea?

The driver can select three energy regeneration levels by operating the KERS switch :
KERS 3: Heavy Heavy Level: Maximum energy is regenerated, the vehicle exhibits shorter coasting distances and a strong sensation of over-run drag or motor braking. The message centre displays KERS 3

Click to expand...

Something I've noticed on long descents is the Kers drops off after a while. I think the power goes to a capacitor first and when that's full the Kers drops to -40 amp as it can't charge the battery fast enough.

Or I could be talking crap.

Redoralive said:

I think the power goes to a capacitor first and when that's full the Kers drops to -40 amp as it can't charge the battery fast enough.

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I'd be very surprised if they have a supercapacitor in there. There is just no need, and they are pretty expensive.

My guess is that after prolonged regeneration, the voltage on one or more cells starts to get excessive, so the BMS warns the motor controller, and the motor controller backs off the regen to keep the cell(s) safe.

Temperature might be having an effect, but regeneration power tends to be lower than drive power, and the battery as to drive way more than half the time. Except in unusual circumstances, and a long descent would certainly be one such circumstance.

So it's probably a combination of cell voltage and battery temperature, and my guess is that cell voltage is the larger component of that.

A similar thing probably happens on long ascents, with the motor controller having to drop the power to prevent cell undervoltage, or again excessive battery temperature. I don't see that reported nearly as often. That's probably because MG's cells can cope much better with discharge currents than with charge currents. You can get burts of well over 100 kW in acceleration, but DC rapid charging doesn't seem to reach that level, even for short periods. Other EV brands seem to be able to do better with DC rapid charging. It's another compromise that makes MGs more affordable, it seems to me. If they put the same type of cells as VW does into Porsches, then the cost would go up, probably significantly.